1. Field of the Invention
The present invention relates to a photoelectric conversion device and a driving method therefor, and more particularly to a photoelectric conversion device provided with a two-dimensional array of reading pixels, adapted for use in a facsimile apparatus, a digital copying apparatus of an X-ray image capture device, and a driving method therefor.
2. Related Background Art
An image reading system utilizing a reduction optical system and a CCD sensor has been conventionally employed for the image capture in the facsimile apparatus, digital copying apparatus or X-ray image capture device, but, based on the recent development of photoelectric semiconductor materials exemplified by hydrogenated amorphous silicon (hereinafter referred to as a-Si), there are conducted active developments for so-called contact sensors having photoelectric converting elements and signal processing units on a large-sized substrate to enable image reading with an optical system of a size same as that of the information source. Particularly a-Si, being usable not only as a photoelectric converting material but also in a thin film field effect transistor (hereinafter written as TFT), provides an advantage that the photoelectric converting semiconductor layer and the semiconductor layer of TFT can be formed simultaneously.
However, in such photoelectric conversion devices, in case of reading a partial area (hereinafter called trimming operation), it is required to drive all the drive lines or all the pixels to read the outputs of all the pixels and then to extract the signals corresponding to the certain required area. For this reason there is encountered a drawback of requiring time for driving the unnecessary drive lines and time for reading the unnecessary output signals.
In case the photoelectric conversion device is of a large area with pixels of a high definition as in the X-ray image capture device, particularly in case of capturing information of a large number of pixels of a high definition as so-called moving image as in the case of observing the image while irradiating the X-ray image capture device continuously with X-rays, such drawback becomes serious because of the significant signal processing time and also because of the increased X-ray radiation dose in case of the X-ray image capture.